Re: Saving Metabolic Energy Seen As Factor In Switch To Bipedalism


... ape-like hominds with chimp-sized brains evolved
bipedalism millions of years before bipedal hominids evolved large
brains.

Well, that depends on the definition of "bipedalism".
1) brain size:
The earliest "large" brain (much larger than in apes) in the fossil
record is Mojokerto, probably c 1.8 Ma. It would have had
as an adult c 800-900 cc (H.Coqueugniot...2004 Nature 431:299).
The ER-1470 skull has recently been re-estimated at (only) c 525 cc.
T.Bromage...2006 http://www.eurekalert.org/multimedia/pub/3572.php
2) "bipedalism":
Walking +-vertically on 2 feet is regularly seen in all apes, esp.in
gibbons, so some form of BPism possibly predates the great/lesser
ape split c 18 Ma.
The humanlike Moroto lumbar vertebra c 19 Ma (with posteriorly placed
transverse process) suggests that a "stiff" & +-vertical spine was
present when great & lesser apes split (A.Filler "The upright ape").
Completely humanlike BPism OTOH seems to be uniquely sapiens, eg,
H.erectus had a somewhat different locomotion, with, eg,
longer & more horizontal femoral necks etc., suggesting, eg,
more frequent abduction of the thighs than in Hs.
No doubt our locomotion evolved "mosaically": all elements at different
times: vertical spine, flat feet, valgus knees, very long legs,
obligatory
two-leggedness, extended legs (vs.BHBK) etc. at different times. Saying
that "BPism evolved (before) X Ma" or so will not help to understand
how our locomotion evolved:
the term "BPism" should be avoided in PA, we should try
to find out when a vertical spine (re)evolved, when short toes, when
valgus knees etc.

As someone who has argued for some time that
bipedalism is as 'old as the hills' an that
it is not special or unique, I would agree
that it has as you say evolved 'mosaically'
in the human animal ... life on the shore
in the context of our shore ancestors probably
added it contribution, to how we get around
on two legs ... today.

Yes.

My hypothesis now:
- hominoid LCA: vertical hanging/floating in densely vegetated swamp forests
c 20 Ma (Morotopith),
- early hominids-pongids: aquarboreal durophagy in coastal forests c 18-10
Ma (peri-Tethys Helio-Austriacopith...),
- early hominids (HPG): + wading & large body in more open coastal
forests/reedbeds (Ourano-Chorora-Nakali-Samburupith c 10-8 Ma),
- Homo: aquarboreal dispersal after H/P split along Ind.Ocean 5-2 Ma,
- "archaic" Homo: + extensive diving 2-0.2 Ma (littoral),
- H.sapiens: wading-walking <200 ka.

Bipedalism: Aaron G. Filler MD, PhD
http://www.uprightape.net/
However the real key to walking upright, having
a relatively large brain and more importantly ...
giving birth, is the pelvis ...

AFAIK the pelvis is no real evol.problem: see A.Schultz's diagrams: birth in
OWMs is as difficult as in humans, it's apes (esp.great apes) that are the
exception: they give birth "easily" (possibly because of the elongation of
their ilia &/or possibly because of relative brain reduction (large body
size)).

Human bipedalism is promoted by a narrow pelvis.

I'd say:
Human cursorialism is promoted by a narrow pelvis.

Apiths had remarkably broad pelvises (& skulls & thoraxes).
H.erectus (still?) had rel.long & horizontal femoral necks.

In stable standing the hip+knee+ankle joints are best on 1 line (as it is in
Hs).
That means that if the femoral neck was longer, the knee had to be more
valgus to be on the line from hip to ankle joint. IOW, more valgus knees are
to be expected when you have broad pelvises (bi-acetabular diameter), long &
horizontal femoral necks (& flaring ilia, for ab/adduction of the thigh),
&/or rel.short femoral shafts (trigonogeometry).
In cursorialism we may expect the leg joints to be as near to the midline as
possible (that's why terrestrial mammals have narrower thoraxes than monkeys
& even more so apes & aquatic mammals esp.in shallow waters (beaver, hippo,
platypus)).
Rel.narrow pelvises & very long femurs & tibias are rel.recent AFAIK (with
the possbile exception of marsh-dwellers like Nariokotome?? wading-birds
have very long legs) & more prevalent in men than in women.

However in mammals the pelvis is also the passage
through which newborn babies pass, and the birth
canal must be sufficiently large to accommodate
a birth. Thus there are evolutionary pressures
favoring a narrow pelvis, efficient in locomotion,
conservative of bone, and less likely to break, but
there are other evolutionary pressures favoring
a wide pelvis, at least in women, allowing the
passage of a developed fetus.
Jordan: Human Birth and Bipedalism
http://tinyurl.com/2aq8fc
---m3d

Interesting website, thanks, m3d.
This seems to be the case when you only compare to apiths/apes, but I
suggest Jordan to read also A.Schultz 1969 "The life of primates" Universe
NY p.154 (incl.comparisons with Macaca etc.).

--Marc Verhaegen
http://allserv.rug.ac.be/~mvaneech/outthere.htm
http://allserv.rug.ac.be/~mvaneech/Symposium.html
http://allserv.rug.ac.be/~mvaneech/Verhaegen.html
http://groups.yahoo.com/group/AAT

.

Relevant Pages

  • Re: Bipedalism in different substrates
    ... >>driven hominid bipedalism, the evidence in extant apes for wading is ... >>even in water shallow enough to move quadrupedally for some unknown ... >>uniquely, for the wading model but, conveniently, not the others. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... >>driven hominid bipedalism, the evidence in extant apes for wading is ... >>even in water shallow enough to move quadrupedally for some unknown ... >>uniquely, for the wading model but, conveniently, not the others. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... >>driven hominid bipedalism, the evidence in extant apes for wading is ... >>even in water shallow enough to move quadrupedally for some unknown ... >>uniquely, for the wading model but, conveniently, not the others. ...
    (sci.anthropology.paleo)
  • Re: Bipedalism in different substrates
    ... >>driven hominid bipedalism, the evidence in extant apes for wading is ... >>even in water shallow enough to move quadrupedally for some unknown ... >>uniquely, for the wading model but, conveniently, not the others. ...
    (sci.anthropology.paleo)
  • Re: human ancestors never passed through a knuckle-walking phase
    ... gibbon, sifaka, penguin, etc. ... knee crawling evolved on soft strata, certainly not in trees or on ... monkeys didn't lose their qpal ground habit, apes did. ... the adaptations necessary for true bipedalism. ...
    (sci.anthropology.paleo)